High power transient events, such as lightning strikes, electrostatic discharge, Electromagnetic Pulses, and Directed Energy Weapon energy, can induce large currents on conductive wiring. This problem becomes compounded when the wiring is installed in less conductive structure such as carbon composite materials as are being widely adopted in the aerospace industry. When conductive wiring is located in explosive or otherwise volatile environments, such as in fuel tanks, the design considerations must take into account product safety and robustness. This is because when high power transient events occur, the wiring can experience and conduct currents up to thousands of amperes.
Many applications of in-tank wiring can typically operate on very small electrical currents (on the order of tens of milliamps or lower), and thus the current capacity of their wiring does not play such an all-important role in their design. However, in situations where the wiring is so proximate to the volatile environment, it becomes far more prudent to use highly resistive wiring that is inherently immune from arcing or sparking.
Moreover, in typical in-tank wiring, the conductive wires are secured to the enclosure walls via nonconductive posts or spacers so that the wires are spaced from and do not lay against the enclosure walls. This technique for installation physically and electrically separates the wiring from the structure to reduce the risk of electrical arcing and sparking in the event of lightning or other high energy transients. This requires additional weight and labor during the build process of aircraft fuel tanks, and such installations require periodic maintenance checks to ensure the nonconductive spacers are free from contamination and the wiring is still secure.
Wiring installed in fuel tanks is not the only wires of concern during lightning strike. A common practice in the aerospace industry is to embed conductive wiring in the bulk of their composite structures. This conductive wiring acts as a continuity sensor for crack detection or crack propagation. In the event of a high power transient electrical event such as lightning strike the conductive wire may be damaged due to arcing/sparking and the associated electrical heating.
It would therefore be highly desirable to have a method and apparatus for preventing ignition of volatile or explosive materials or gases in protective environments resulting from high current transient events causing arcing or sparking to electrical wires.
Further it would be highly desirable to have a method and an apparatus that would permit detection of the formation or propagation of cracks in structures exposed to a structural environment that is not susceptible to damage or destruction by electrical transient environments.